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Global long-term observations of coastal erosion and accretion - PubMed

  • ️Mon Jan 01 2018

Global long-term observations of coastal erosion and accretion

Lorenzo Mentaschi et al. Sci Rep. 2018.

Abstract

Changes in coastal morphology have broad consequences for the sustainability of coastal communities, structures and ecosystems. Although coasts are monitored locally in many places, understanding long-term changes at a global scale remains a challenge. Here we present a global and consistent evaluation of coastal morphodynamics over 32 years (1984-2015) based on satellite observations. Land losses and gains were estimated from the changes in water presence along more than 2 million virtual transects. We find that the overall surface of eroded land is about 28,000 km2, twice the surface of gained land, and that often the extent of erosion and accretion is in the order of km. Anthropogenic factors clearly emerge as the dominant driver of change, both as planned exploitation of coastal resources, such as building coastal structures, and as unforeseen side effects of human activities, for example the installment of dams, irrigation systems and structures that modify the flux of sediments, or the clearing of coastal ecosystems, such as mangrove forests. Another important driver is the occurrence of natural disasters such as tsunamis and extreme storms. The observed global trend in coastal erosion could be enhanced by Sea Level Rise and more frequent extreme events under a changing climate.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1

Overall gained and lost (a), and gained-lost neat balance (b) of land and active zone, aggregated by continent/ocean and expressed in km2 and in cross-shore distance. The global aggregated quantities are also shown in both panels. Coastline colors identify the considered areas. This figure was generated with the MATLAB programming language.

Figure 2
Figure 2

Size distribution of cross-shore transition length above 50 m, for erosion and accretion of land (a) and active zone (b). Lost (c) and gained (d) land around the world; lost (f) and gained (g) active zone; balance gained - lost land (e) and active zone (h). Maps show the length of cross-shore erosion and accretion aggregated on coastal segments of 100 km. In all the maps the 4 spots with the highest local transition along a 250 m transect are indicated. This figure was generated with the MATLAB programming language.

Figure 3
Figure 3

List of local cases of erosion/accretion discussed in this manuscript or used for the dataset validation. The legend provides for each spot a brief summary of the drivers of shoreline change.

Figure 4
Figure 4

Satellite images of locations characterized by strong morphological change, at the beginning and at the end of the considered period, and time series of the cross-shore erosion/accretion. Mekong delta (a–c), Shanghai (d–f), the city of Banda Aceh (Indonesia, g–i), Mississippi delta (j–l). The red lines in panels abdeghjk mark the coastline in the first year of observations. In panels cfil the time of relevant events is marked with a red line. This figure was generated using data from the USGS (

http://earthexplorer.usgs.gov/

), Copernicus Sentinel data 2016–2017, the Google-Earth-Engine, and the programming languages python and MATLAB.

Figure 5
Figure 5

Satellite images of locations characterized by strong morphological change and maps of the observed transitions. Indus delta (a), Southern Bohai sea (b), the Reentrâncias Maranhenses (NE Brazil, c–e), the Fakarava island (French Polynesia, f) the Northern part of the Choiseul island (Solomon, g), Atyrau (Caspian sea, Kz, h–j). This figure was generated using data from the USGS (

http://earthexplorer.usgs.gov/

), Copernicus Sentinel data 2016–2017, the Google-Earth-Engine, and the programming languages python and MATLAB.

Figure 6
Figure 6

Satellite images of locations characterized by strong morphological change, at the beginning and at the end of the considered period, and time series of the cross-shore erosion/accretion. Mexican California (a–c), Semarang (Indonesia, d–f), Hudson Bay (Canada, g–i). The red lines in panels abdegh mark the coastline in the first year of observations. In panel c the ENSO index multiplied by (−1) is superimposed with the erosion series and their correlation coefficient ρ is indicated. This figure was generated using data from the USGS (

http://earthexplorer.usgs.gov/

), Copernicus Sentinel data 2016–2017, the Google-Earth-Engine, and the programming languages python and MATLAB.

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